The character known as the Countess Werdenberg from the anime Gilgamesh has the real name Hiroko Kageyama. Her past is deeply rooted in the scientific research facility called Heaven's Gate, where she worked closely with the brilliant scientist Terumichi Madoka. She harbored strong romantic feelings for Madoka, but he was already married with a daughter, making her love unattainable. In what seems to be an act born from heartbreak, she instead married a wealthy scientist and Count who was her colleague, taking on the title of Countess. The catastrophic event known as Twin X, caused by Madoka's direct contact with the mysterious life form Tear, resulted in the death of her husband, allowing her to inherit his vast fortune.

Following the disaster, the Countess was one of the sole survivors from Heaven's Gate and fell into a coma for several years. Upon awakening, she dedicated herself to finding children rumored to possess extraordinary psychic powers known as Dynamis. She located three such children, rescued them from miserable circumstances, and raised them as her own, forming a group known as the Orga-Superior. The Countess is a formal and enigmatic figure who rarely smiles and never speaks of her past, always dressed in a manner befitting her aristocratic title. Despite having a mansion, she chooses to live in a large, luxurious hotel where she maintains an air of elegance and strict routine, such as holding formal dinners with her makeshift family each night.

The Countess's primary motivation is not altruism but is deeply personal and driven by her unresolved feelings for Terumichi Madoka. She opposes Madoka, who has transformed into a being named Enkidu and leads the superhuman Gilgamesh, hoping to bring about a cleansing flood to end humanity. Her war against the Gilgamesh is a direct extension of her past with Madoka. This personal obsession heavily colors her key relationships. She despises Kiyoko, Madoka's daughter, most likely because the girl is the living product of the man she loved with another woman. Conversely, she is notably warmer toward Kiyoko's brother, Tatsuya, because he is the spitting image of his father, Terumichi. She keeps the Orga-Superior children loyal to her, but she does not share her true reasons for the conflict with them, using them as instruments in her personal vendetta.

The Countess herself possesses the ability to use Dynamis, a power she gained when cloned pieces of her own body that had been contaminated by Tear were implanted to save her life. However, she uses this power extremely sparingly, either by choice or perhaps because she cannot wield it outside of the most dangerous situations. Her character undergoes a dramatic and tragic development as the series concludes. She eventually discovers the shattering truth that her own heart was the source of Tear, and that the embryos at Heaven's Gate were contaminated because of her own intense hatred and jealousy toward Terumichi's wife. This revelation reveals that she is the unwitting cause of the very apocalypse she has been fighting. In the final battle, she kills multiple key characters before finally surrendering her one-woman war, allowing Tear to fully enter her body and initiate the cleansing flood that ends the human world. Her final tragic act leads to the world's destruction, cementing her role not just as a powerful aristocrat in a post-apocalyptic struggle, but as a tragic figure whose actions were driven by a jealous and broken heart.